src/partition_alloc/partition_alloc-inl.h

// Copyright 2020 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef PARTITION_ALLOC_PARTITION_ALLOC_INL_H_
#define PARTITION_ALLOC_PARTITION_ALLOC_INL_H_

#include <cstring>

#include "partition_alloc/build_config.h"
#include "partition_alloc/buildflags.h"
#include "partition_alloc/in_slot_metadata.h"
#include "partition_alloc/partition_alloc_base/compiler_specific.h"
#include "partition_alloc/partition_alloc_base/cxx_wrapper/algorithm.h"
#include "partition_alloc/partition_alloc_config.h"
#include "partition_alloc/random.h"
#include "partition_alloc/tagging.h"
#include "partition_alloc/thread_isolation/thread_isolation.h"

// Prefetch *x into memory.
#if defined(__clang__) || PA_BUILDFLAG(PA_COMPILER_GCC)
#define PA_PREFETCH(x) __builtin_prefetch(x, 0)
#else
#define PA_PREFETCH(x)
#endif

#if defined(__clang__) || PA_BUILDFLAG(PA_COMPILER_GCC)
#define PA_PREFETCH_FOR_WRITE(x) __builtin_prefetch(x, 1)
#else
#define PA_PREFETCH_FOR_WRITE(x)
#endif

namespace partition_alloc::internal {

// This is a `memset` that resists being optimized away. Adapted from
// boringssl/src/crypto/mem.c. (Copying and pasting is bad, but //base can't
// depend on //third_party, and this is small enough.)
#if PA_CONFIG(IS_NONCLANG_MSVC)
// MSVC only supports inline assembly on x86. This preprocessor directive
// is intended to be a replacement for the same.
//
// TODO(crbug.com/40234441): Make sure inlining doesn't degrade this into
// a no-op or similar. The documentation doesn't say.
#pragma optimize("", off)
#endif
PA_ALWAYS_INLINE void SecureMemset(void* ptr, uint8_t value, size_t size) {
  PA_UNSAFE_TODO(memset(ptr, value, size));

#if !PA_CONFIG(IS_NONCLANG_MSVC)
  // As best as we can tell, this is sufficient to break any optimisations that
  // might try to eliminate "superfluous" memsets. If there's an easy way to
  // detect memset_s, it would be better to use that.
  __asm__ __volatile__("" : : "r"(ptr) : "memory");
#endif  // !PA_CONFIG(IS_NONCLANG_MSVC)
}
#if PA_CONFIG(IS_NONCLANG_MSVC)
#pragma optimize("", on)
#endif

#if PA_BUILDFLAG(EXPENSIVE_DCHECKS_ARE_ON)
// Used to memset() memory for debugging purposes only.
PA_ALWAYS_INLINE void DebugMemset(void* ptr, int value, size_t size) {
  // Only set the first 512kiB of the allocation. This is enough to detect uses
  // of uininitialized / freed memory, and makes tests run significantly
  // faster. Note that for direct-mapped allocations, memory is decomitted at
  // free() time, so freed memory usage cannot happen.

#if PA_BUILDFLAG(ENABLE_THREAD_ISOLATION) && PA_BUILDFLAG(ENABLE_PKEYS)
  LiftThreadIsolationScope lift_thread_isolation_restrictions;
#endif
  size_t size_to_memset = std::min(size, size_t{1} << 19);
  PA_UNSAFE_TODO(memset(ptr, value, size_to_memset));
}
#endif  // PA_BUILDFLAG(EXPENSIVE_DCHECKS_ARE_ON)

PA_ALWAYS_INLINE uintptr_t ObjectInnerPtr2Addr(const void* ptr) {
  return UntagPtr(ptr);
}

// In order to resolve circular dependencies, define template method:
// GetMetadataOffset() here and SlotSpanMetadata::FromAddr(),
// SuperPageExtentEntry's SuperPageBeginFromExtent() ... use it.
template <typename T>
std::ptrdiff_t GetMetadataOffset([[maybe_unused]] const T* root) {
#if PA_CONFIG(MOVE_METADATA_OUT_OF_GIGACAGE)
#if PA_BUILDFLAG(DCHECKS_ARE_ON)
  PA_DCHECK(root);
#endif  // PA_BUILDFLAG(DCHECKS_ARE_ON)
  return root->MetadataOffset();
#else
  return static_cast<std::ptrdiff_t>(SystemPageSize());
#endif  // PA_CONFIG(MOVE_METADATA_OUT_OF_GIGACAGE)
}

PA_ALWAYS_INLINE uintptr_t
PartitionSuperPageToMetadataPage(uintptr_t super_page,
                                 [[maybe_unused]] std::ptrdiff_t offset) {
#if PA_CONFIG(MOVE_METADATA_OUT_OF_GIGACAGE)
  return super_page + static_cast<uintptr_t>(offset);
#else
  return super_page + SystemPageSize();
#endif  // PA_CONFIG(MOVE_METADATA_OUT_OF_GIGACAGE)
}

PA_ALWAYS_INLINE uintptr_t
PartitionMetadataPageToSuperPage(uintptr_t metadata_page,
                                 [[maybe_unused]] std::ptrdiff_t offset) {
#if PA_CONFIG(MOVE_METADATA_OUT_OF_GIGACAGE)
  return metadata_page - static_cast<uintptr_t>(offset);
#else
  return metadata_page - SystemPageSize();
#endif  // PA_CONFIG(MOVE_METADATA_OUT_OF_GIGACAGE)
}

}  // namespace partition_alloc::internal

#endif  // PARTITION_ALLOC_PARTITION_ALLOC_INL_H_